Source : Webster's Revised Unabridged Dictionary (1913)

Blissful \Bliss"ful\, a.
   Full of, characterized by, or causing, joy and felicity;
   happy in the highest degree. ``Blissful solitude.'' --Milton.
   -- {Bliss"ful*ly}, adv. -- {Bliss"ful*ness}, n.

Source : WordNet®

blissfully
     adv : in a blissful manner; "he was blissfully unaware of the
           danger"